"Once identified by staff, the exchange was put into maintenance while we assessed damages," it said.

Police and the High-Tech Crimes Unit were then notified. Cryptopia said it was being investigated as a "major crime".

Police said a significant value of virtual currency may be involved and they were talking to the company.

They said the investigation related to potential unauthorised transaction activity and although the investigation was in early stages it was being taken very seriously.

A Christchurch-based investigation team was being established including specialist police staff with expertise in the area, they said, and they were also liaising with relevant partner agencies in New Zealand and overseas.

Trading on the site would remain in maintenance mode and would be suspended until investigations were completed, Cryptopia said.

Bitcoin fell to a more than one-year low today, breaching a key support level of $6000 and causing a wave of selling in the digital currency and other crypto assets in what has been a prolonged market…